Microstructural changes and the understanding of their effect on photocurrent generation are key aspects for improving the efficiency of organic photovoltaic devices. We analyze the impact of a systematically increased amount of the solvent additive diiodooctane (DIO) on the morphology of PBDTTT-C:PC71BM blends and related changes in free carrier formation and recombination by combining surface imaging, photophysical and charge extraction techniques. We identify agglomerates visible in AFM images of the 0% DIO blend as PC71BM domains embedded in an intermixed matrix phase. With the addition of DIO, a decrease in the size of fullerene domains along with a demixing of the matrix phase appears for 0.6% and 1% DIO. Surprisingly, transient absorption spectroscopy reveals an efficient photogeneration already for the smallest amount of DIO, although the largest efficiency is found for 3% DIO. It is ascribed to a fine-tuning of the blend morphology in terms of the formation of interpenetrating donor and acceptor phases minimizing geminate and nongeminate recombination as indicated by charge extraction experiments. An increase in the DIO content to 10% adversely affects the photovoltaic performance, most probably due to an inefficient free carrier formation and trapping in a less interconnected donor-acceptor network.

In order to produce materials with tailored structures and functions via supramolecular self-assembly of molecular precursors in a predictable fashion, it is necessary to develop 'supramolecular methods' based on structurally simple 'supramolecular synthons'. Thus, the formation of one-dimensional aggregates from p-conjugated molecules requires a combination of non-covalent interactions that efficiently suppresses lateral aggregation, promotes one-dimensional aggregation, and is also compatible with a productive p-p overlap of the constituent molecules. In the present work, we demonstrate that oligopeptide-polymer derivatives comprising a flexible polymer segment terminally attached to a b-sheet-forming oligopeptide segment are structurally simple substituents that perfectly fulfill these requirements. We synthesized a matrix of diacetylene model compounds that carried oligopeptide-polymer substituents with varying degrees of polymerization of the attached polymers and different length oligopeptide segments. We combined solution-phase IR spectroscopy, AFM imaging and the topochemical diacetylene polymerization as a highly sensitive probe for the molecular arrangement and the degree of order inside aggregates obtained in organic solvents. The thus determined molecular parameters for the reliable formation of well-defined nanoscopic fibrillar structures with uniform diameters, and defined helical 'core-shell' morphologies were then successfully transferred to analogous perylene bisimide and quaterthiophene derivatives, demonstrating the versatility and robustness of the chosen molecular design.

The distribution of water within the supramolecular structure of collagen fibrils is important for understanding their mechanical properties as well as the biomineralization processes in collagen-based tissues. We study the influence of water on the shape and the mechanical properties of reconstituted fibrils of type I collagen on the nanometer scale. Fibrils adsorbed on a silicon substrate were imaged with multiset point intermittent contact (MUSIC)-mode atomic force microscopy (AFM) in air at 28% relative humidity (RH) and in a hydrated state at 78% RH. Our data reveal the differences in the water uptake between the gap and overlap regions during swelling. This provides direct evidence for different amounts of bound and free water within the gap and overlap regions. In the dry state, the characteristic D-band pattern visible in AFM images is due to height corrugations along a fibril's axis. In the hydrated state, the fibril's surface is smooth and the D-band pattern reflects the different mechanical properties of the gap and overlap regions.

High resolution volume images of semicrystalline polypropylene were obtained by stepwise wet-chemical etching followed by atomic force microscopy of the specimen. Enhanced signal-to-noise ratio and spatial resolution were achieved by using the second flexural eigenmode of the cantilever for phase imaging while the amplitude of the first mode was used as feedback signal. The energy dissipated between the tip and the sample revealed characteristic differences between the crystalline and the amorphous regions of the polypropylene after etching, indicating the presence of a thin (<10nm thick) amorphous layer on top of crystalline regions.

The energy dissipated between tip and sample during dynamic atomic force microscopy (AFM) is a sensitive measure of local surface properties. We mapped the surface properties of crystalline and amorphous regions in thin films of different kinds of elastomeric polypropylene (ePP) with 10 nm lateral resolution. The dissipated energy as a function of the amplitude setpoint displays discriminative shapes for both polymer regions. Differences in the shape as well as in the maximum amount of dissipated energy are interpreted as different amounts of amorphous material on top of crystalline regions. Indentation experiments at different amplitude setpoints resulted in indentation depths of the AFM tip up to 11 nm, on both crystalline and amorphous regions. This and the change of dissipated energy upon wet chemical etching indicate that crystalline regions are covered by an up to 10 nm thick amorphous layer.